Electrical trigger circuit



March 12, 1963 s, SIMON 3,081,419

ELECTRICAL TRIGGER CIRCUIT Filed April 14 1959 I Inventor S Simon yWM)Attorney United States Patent 3,081,419 ELECTRICAL TRIGGER CIRCUITStephane Marcel Simon, Antwerp, Belgium, assiguor to InternationalStandard Electric Corporation, New York, N.Y., a corporation of DelawareFiled Apr. 14, 1959, Ser. No. 806,278 7 Claims priority, applicationBelgium Apr. 28, 1958 6 Claims. (Cl. 317-148.5)

The invention relates to an electrical trigger circuit and moreparticularly to a circuit including two transistors of opposedconductibilities and being able to be in two distinct electricalconditions.

Such circuits can be used for various purposes and particularly intelecommunication equipments to operate relays.

Trigger circuits using transistors are already known and reference canfor instance be made to US. Patent No. 2,744,198 where two transistorsof opposite type are used. However, according to these known circuits,the operation is similar to an Eccles-Jordan circuit, i.e. the twodistinct electrical conditions correspond to a reversal of the conditionof the two transistors, but one of them is always conductive, while theother is locked or non-conductive.

An object of the invention is to realize an electrical trigger circuitparticularly well adapted to reveal the momentary application of anelectrical signal of very short duration in order to operate a relay,the order of magnitude of the duration of this electrical signal beingdistinctly less than the operation time of a telephone type relay.

Another object of the invention is to realize an electrical triggercircuit adapted to produce the operation of a relay after a certainpredetermined time.

According to a first characteristic of the invention, an electricaltrigger circuit as defined aboveis character ized in that the twodistinct electrical conditions of this circuit correspond respectivelyto the two transistors being non-conductive or to the two transistorsbeing conductive.

According to another characteristic of the invention, an electricaltrigger circuit as characterized above is characterized in that the baseof the first transistor is coupled to the collector of the secondtransistor and vice-versa.

The objects and characteristics of the invention mentioned above as wellas others, will become more apparent by referring to the followingdetailed description of a preferred embodiment of the invention read inconjunction with the accompanying drawing and which represents a triggercircuit adapted to operate either as timing device or as a circuitreacting on very short current pulses.

The circuit will first of all be described in assuming that capacitor Cis not inserted in the circuit and that the circuit is adapted to causethe operation of relay.

Tr during a very short-contact interruption normally ensured by a pulsesource here shown generally as key K This situation can for instancetake place in telephone exchanges and more particularlywhen aregistering circuit wantsto cause the operation of a relay due to theoperation of a change-over contact of a relay, which may be part of thecircuit controlled from this register. When it is necessary to reveal egthe operation of a relay forming part of a selector circuit of atelephone system, the contact in its rest position can normally give aground to the register, but as soon as the relay is operated, thechangeover contact in its work position can again be connected to aground. From this moment on, the operation of the selector relay cannotbe revealed by the simple momentary interruption of the ground. Theshown circuit is particularly well adapted to this use since it permitsthe operation of relay Tr on condition that key K is open only during afew hundredths of a microsecond.

When the circuit is put into service, contact k is closed thus causingthe connection of the voltage divider, constituted by resistances R to Rin series, between earth at contact k and the negative battery of 48volts. By way of example various potentials have been indicated at thepotentiometer terminals;

The least negative potential i.e. -27 volts is connected to the base ofa first transistor T of the p-n-p type, through an electromechanicalload circuit such as the winding of relay Tr in series with theresistances R and R This potential is also connected across the Windingof relay Tr to the collector of a second transistor T of the n-p-n type.The next potential of 27.5 volts is directly connected to the emitter oftransistor T the next potential of 4l.5 volts is directly connected tothe emitter of transistor T 2 whereas the most negative potential of-42.5 volts is connected to the base of transistor T via resistance Rthis base being moreover coupled to the collector of transistor T1across resistance R The ground being normally applied to the cathode ofrectifier S by means of key K and the anode of this rectifier beingconnected to the junction point of resistances R and R the rectifier isnormally blocked. Moreover, the emitter-base circuits of the twotransistors are so biased that neither of them is conductive in the restcondition of the circuit. I

When key K even momentarily opens, the cathode of rectifier S is nowconnected to the negative battery of 48 volts across resistance R and acurrent flows immediately in the emitter-base circuit of transistor TThe emitter current of transistor T is amplified in thecollector'circuit of this transistor and reaches the base of transistorT across resistance R to be again amplified in the collector of thislast transistor. The greater part of the amplified current flows throughthe winding of relay Tr which operates while the rest of the amplifiedcurrent flows in the base of transistor T via resistances R andR The twotransistors thus become conductive due to a cumulative effect and theycontinue to energize each other, this action being independent from theinitial trigger current.

By Way of example, the values of the resistances R to R can be 510 ohms,10 ohms, 270 ohms, 20 ohms, ohms, kilo ohms, 10 kilo ohms, 7.5 kilo ohmsand 18 kilo ohms.

Means are provided for applying on or off signals a selected timeinterval after operation of the pulse source key K thereby controllingthe operate time of relay Tr. Thus, if the circuit has to be used fortiming delays for instance in a telephone exchange register in order tocause the automatic release of the register after a certain time ofoccupation, capacitor C is connected in parallel with resistance R Inthis case, the capacitor is initially charged to the full voltage of thebattery, while key K remains closed. When opening thiskey, capacitor Cdischarges exponentially across resistance R and as soon as thepotential at the cathode of rectifier S is more negative than 27.5volts, a' current starts flowing in the base of transistor T whichproduces the cumulative trigger effect already mentioned above,

By using a capacitor of 50 microfarads and a value of 1.5 'megohms forresistance R one could for instance obtain delay times of the order ofvarious tenths of seconds.

While the principles of the invention havebeen described above inconnection with specific apparatus, it is 3 to be clearly understoodthat this description is made only by way of example and not as alimitation on the scope of the invention.

I claim:

1. An electrical trigger circuit comprising a PNP transistor and an NPNtransistor, each transistor having base, collector, and emitterelectrodes, means including at least one resistance for coupling thebase of each transistor to an electrode of the other transistor so thatcurrent flowing through the emitter-collector circuit of each transistoris amplified by the other transistor, whereby said two transistors forma bistable circuit, means comprising a voltage pulse source for applyinga reference voltage to an electrode of one of said transistors, meansfor applying a control voltage to the base electrode of said onetransistor whereby said one transistor switches on or off responsive tochanges in the polarity of said control voltage relative to saidreference voltage, means associated with said control voltage applyingmeans for selecting the time required for said one transistor to switchon or off, and load circuit means controlled by current in theemitter-collector circuit of the other transistor when said onetransistor is switched on.

2. The circuit of claim 1 wherein said load circuit comprises thewinding of electro-mechanical means and said control voltage is suppliedby a pulse source.

3. The circuit of claim 2 and a two terminal source of potential, a fourterminal voltage divider connected across said two terminals of saidsource, said four terminals being connected to the collector of saidother transistor, the emitter of said one transistor, the emitter ofsaid other transistor, and the collector of said one transistor toprovide graduated bias potentials in the order named.

4. The circuit of claim 3 wherein said time selecting means comprises acapacitor in series with a rectifier also connected to said oneresistance for controlling the rise time of voltage from said pulsesource, said rectifier being poled to be momentarily back biased by avoltage on said capacitor during said rise time and then forwardlybiased after said rise time, thereby controlling the operate time ofsaid electro-mechanical means.

5. An electrical trigger circuit comprising a PNP transistor and an NPNtransistor, each transistor having base, collector, and emitterelectrodes, means including at least one resistance for coupling thebase of each transistor to an electrode of the other transistor so thatcurrent flowing through the emitter-collector circuit of each transistoris amplified by the other transistor, whereby said two transistors forma bistable circuit, means comprising a voltage pulse source for applyinga reference voltage to an electrode of one of said transistors, meansfor applying a control voltage to the base electrode of said onetransistor whereby said one transistor switches on or off responsive tochanges in the polarity of said control voltage relative to saidreference voltage, load circuit means controlled by current in theemitter-collector circuit of the other transistor when said onetransistor is switched on, said load circuit comprising the winding ofelectromechanical means, two terminal sources of potential, a fourterminal voltage divider connected across said two terminals of saidsource, said four terminals being conto the junction between said seriesconnected resistors.

6. The circuit of claim 5 and means comprising a capacitor alsoconnected to the junction between said resistors for controlling therise time of voltage from said pulse source, thereby controlling theoperate time of said electromechanical means.

References Cited in the file of this patent UNITED STATES PATENTS2,840,727 Guggi June 24, 1958 2,866,106 Schuh Dec. 23, 1958 2,890,353Van Overbeek et al June 9, 1959 2,971,134 Cockrell Feb. 7, 19612,997,632 Shepard Aug. 22, 1961 3,034,024 Mierendorf et a1 May 8, 1962.

OTHER REFERENCES Loyd P. Hunter: Handbook of Semiconductor Electronics,page 15-52, Oct. 15, 1956.

1. AN ELECTRICAL TRIGGER CIRCUIT COMPRISING A PNP TRANSISTOR AND AN NPN TRANSISTOR, EACH TRANSISTOR HAVING BASE, COLLECTOR, AND EMITTER ELECTRODES, MEANS INCLUDING AT LEAST ONE RESISTANCE FOR COUPLING THE BASE OF EACH TRANSISTOR TO AN ELECTRODE OF THE OTHER TRANSISTOR SO THAT CURRENT FLOWING THROUGH THE EMITTER-COLLECTOR CIRCUIT OF EACH TRANSISTOR IS AMPLIFIED BY THE OTHER TRANSISTOR, WHEREBY SAID TWO TRANSISTORS FORM A BISTABLE CIRCUIT, MEANS COMPRISING A VOLTAGE PULSE SOURCE FOR APPLYING A REFERENCE VOLTAGE TO AN ELECTRODE OF ONE OF SAID TRANSISTORS, MEANS FOR APPLYING A CONTROL VOLTAGE TO THE BASE ELECTRODE OF SAID ONE TRANSISTOR WHEREBY SAID ONE TRANSISTOR SWITCHES "ON" OR "OFF" RESPONSIVE TO CHANGES IN THE POLARITY OF SAID CONTROL VOLTAGE RELATIVE TO SAID REFERENCE VOLTAGE, MEANS ASSOCIATED WITH SAID CONTROL VOLTAGE APPLYING MEANS FOR SELECTING THE TIME REQUIRED FOR SAID ONE TRANSISTOR TO SWITCH "ON" OR "OFF," AND LOAD CIRCUIT MEANS CONTROLLED BY CURRENT IN THE EMITTER-COLLECTOR CIRCUIT OF THE OTHER TRANSISTOR WHEN SAID ONE TRANSISTOR IS SWITCHED ON. 